A modifier dangles if the implied subject of an introductory
clause or phrase differs from the actual subject.

Dangling gerunds

Below are examples of dangling gerunds
(gerunds are similar to participles in that they end in ing,
but gerunds act as nouns rather than as adjectives - in these examples,
the gerunds are objects of prepositional phrases).

example: While
drinkinggerund our
coffee, the lions approached our camp.
The implied subject of drinking
is 'we' or 'whoever' is in camp, but the actual subject is the 'lions'.
Correct this by making 'we' the implied subject and actual subject
- While
drinking our coffee, we saw the lions approach our
campor
by converting the gerund phrase into a clause - While
we were drinking coffee, the lions approached our camp.

example: After
reviewinggerund
the data, it was concluded that the experiment was poorly designed.
The actual subject of reviewing
is it, but the implied subject is whoever reviewed the data
- After
reviewinggerund
the data, the panel concluded that the experiment was poorly designed.

example: Before
samplinggerundthe extract, pH was determined.Clarify
this as before - Before
sampling the extract, we determined its pH or Before
the extract was sampled, pH was determined.

example: By
havinggerund the
subject perform an action, instead of receivinggerund
an action as in the passive voice, the purpose of the sentence is
clearer. The implied subject
for having and receiving is either the writer
or the sentence but is not the purpose. So,
having and receiving dangle.
By having the subject perform an action, the writer clarifies
the purpose of the sentence.

example: The specimens were examined usingpresent participle a light microscope. (The specimens were examined with a light microscope.)

Dangling past participles (past
participles usually end in ed)

example: Trainedpast participle in soil
ecology, the research team's approach emphasized bacteria and fungi.
The implied subject of trained is research
team, not approach. (Trainedpast
participle in soil ecology, the research team emphasized
bacteria and fungi.)

example: Surprisingly,
the molecular systematics of Mysticeti [a suborder of whales] have
received little attention. Although generally thought past
participleto include only 10-12 species, questions
remain about the systematic relationships within this suborder.
The implied subject of
the past participle thought is suborder - it is the
suborder that is thought to include - but the subject of
the independent clause is questions. (Although
generally thought past participleto include only 10-12 species, this suborder may contain many
more.)

example: This
course provides an introduction to air pollution problems groundedpast participlein
physical and chemical fundamentals. The implied
subject of the past participle grounded is introduction,
not problems. Also note the ineffective contrast of air
pollution and grounded.

Dangling infinitives

I was unaware
that infinitive phrases could dangle until an editor pointed this out
to me. The problem is the same as with dangling gerunds and participles:
the phrase introduces an action that should be linked to an actor,
an actor who should appear as the subject of the following clause.
The infinitive dangles or is poorly attached if the subject of the
following clause is someone or something who did not do the action
in the infinitive.

example: To
determine whether pH changed through time, soil was sampled
monthly. The actual subject of the main clause
is soil but the implied subject is whoever was determining
soil pH.

Dangling infinitives are very common
in scientific writing because scientists often use passive
voice to describe methods; the actor implied by the infinitive
simply dissappears in the passive voice clause. Dangling infinitives
are so common that few would recognize them as being wrong, and
many would argue that they are not wrong, that the sentence form
(infinitive plus passive voice) is now standard in scientific writing
and that the infinitive invokes an actor but does not require that
the actor be explicitly named.

The easiest way to correct a dangling
infinitive is to use active voice.

example: To
determine whether pH changed through time, we sampled the soil
monthly. But first person/active voice can be
jarring if the paper has not used first person and if the Methods
are mostly in passive voice. Perhaps this is yet another reason
to use more active voice and more first person in scientific writing.

How about relocating the infinitive
phrase? Soil
was sampled monthly to determine whether pH changed through
time. According to the staff at the Chicago
Manual of Style, relocation doesn't help, i.e., the infinitive
still dangles.

Other
solutions are problematic.

Changes in
pH through time were determined by sampling soil monthly.

For determining
changes in pH through time, soil was sampled monthly.

As I indicated, dangling infinitives are very common in scientific writing. If I indicate that your paper contains dangling infinitives, you could decide to leave them as they are, especially if they are in the Methods section or if they otherwise concern methods. Few reviewers, editors, and readers will consider them a problem. Still, you should recognize them and understand how to change them if you want to or if you are forced to by an editor.

Update: On 21 November 2010, I was consulting the 7th edition (2006) of Scientific Style and Format: the CSE Manual for Authors, Editors, and Publishers, which is published by the Style Manual Committee of the Council of Science Editors. This book is considered authoritative with respect to scientific writing. I came upon the following dangling infinitives:

Page 145: To avoid potential confusion about the meaning of the comma, the following style is recommended. (on page 145)

To facilitate prompt binding of the issues of a volume, the title page, the volume table of contents, …., are usually published as the end pages of the last issue of the volume. (on page 448).

Summary

As always, our emphasis here is on clarity
rather than on grammatical correctness. In most of the above examples,
the dangling elements will distract and or slow the attentive reader.
He or she will be able to decipher the sentence, but they will have to
work more than necessary. To decide whether an element is dangling,
read your sentences as an attentive reader would.

Some dangling participles have become standard
and are no longer considered dangling. See Garner (A Dictionary of
Modern American Uses) for more examples and explanation of 'acceptable
danglers'.

example: Assuming
the equipment arrives, the experiment will continue.

example: Considering
the significance of the data, the experiment will be repeated.

example: Regarding
the experiment, proper controls will be included.

example: According
to the methods section, the experiment lacked a control.